PREPLANING BUILDING HAZARDS
BY FRANCIS L. BRANNIGAN, SFPE
Editor`s note: For further reference, consult Building Construction for the Fire Service (BCFS3), Third Edition. Page numbers are included after each caption for your convenience.
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(Top) Brick veneer walls consist of a single wythe (one vertical thickness of masonry) of brick. They aren`t load bearing and are inherently unstable. They depend entirely on the basic wall for support. The building should not be thought of as a “brick” building but as a wooden (usually), steel, or concrete (less frequently) building. At one time you could tell brick veneer from load-bearing brick masonry because every seventh course (horizontal layer) of brick was laid as headers (end exposed), whereas brick veneer was laid as all stretchers (side exposed). The development of wire trusses embedded in the mortar made it possible to lay a solid masonry wall as all stretchers, so there is no visible distinction between the two. (Ref. pp 122-124)
Thanks to Firefighter Eric Norberg of Warwick, Rhode Island, for this photo.
(Second) Wood floors with a gypsum ceiling can get a one-hour fire resistive label from UL. When they pass the ASTM E 199 test, however, the test is conducted with an average static floor load of 30 to 40 psf. Two Salt Lake County firefighters with full gear weigh about 450 pounds, a dynamic impact load over possibly nine square feet. The fire resistance ratings of wood and gypsum assemblies have many other deficiencies. (Ref.?)
(Third) Connections are important in building stability. Note how the gusset plates have fallen off these roof trusses. They are in imminent danger of collapse. Only a foolhardy photographer would stand under these failing trusses to get a picture for your instruction. (Ref. pp 80-86)
(Bottom) As designers strive for larger and larger clear span areas, trusses on trusses become more common. Note that the bottom chord of the huge truss is composed of three 2 ¥ 10 members. All the butt joints are at the same location. A better design would be to stagger the joints and bolt the 2 ¥ 10s together. A fire-caused failure at this point will bring down the entire structure. Check your local Denny`s restaurant. Some I have seen have trusses on trusses. For another view of this truss, see page 527 of BCFS3.
FRANCIS L. BRANNIGAN, SFPE, recipient of Fire Engineering`s first Lifetime Achievement Award, has devoted more than half of his 56-year career to the safety of firefighters in building fires. He is well known for his lectures and videotapes and as the author of Building Construction for the Fire Service, Third Edition, published by the National Fire Protection Association. Brannigan is an editorial advisory board member of Fire Engineering. He may be reached at (301) 855-1982.
